Isotopic signatures of anthropogenic CH<inf>4</inf> sources in Alberta, Canada: Fid-Bau Portal

Isotopic signatures of anthropogenic CH4 sources in Alberta, Canada

Lopez, M. / Sherwood, O.A. / Dlugokencky, E.J. / Kessler, R. / Giroux, L. / Worthy, D.E.J.

AbstractA mobile system was used for continuous ambient measurements of stable CH4 isotopes (¹²CH4 and ¹³CH4) and ethane (C2H6). This system was used during a winter mobile campaign to investigate the CH4 isotopic signatures and the C2H6/CH4 ratios of the main anthropogenic sources of CH4 in the Canadian province of Alberta. Individual signatures were derived from δ¹³CH4 and C2H6 measurements in plumes arriving from identifiable single sources. Methane emissions from beef cattle feedlots (n = 2) and landfill (n = 1) had δ¹³CH4 signatures of −66.7 ± 2.4‰ and −55.3 ± 0.2‰, respectively. The CH4 emissions associated with the oil or gas industry had distinct δ¹³CH4 signatures, depending on the formation process. Emissions from oil storage tanks (n = 5) had δ¹³CH4 signatures ranging from −54.9 ± 2.9‰ to −60.6 ± 0.6‰ and non-detectable C2H6, characteristic of secondary microbial methanogenesis in oil-bearing reservoirs. In contrast, CH4 emissions associated with natural gas facilities (n = 8) had δ¹³CH4 signatures ranging from −41.7 ± 0.7‰ to −49.7 ± 0.7‰ and C2H6/CH4 molar ratios of 0.10 for raw natural gas to 0.04 for processed/refined natural gas, consistent with thermogenic origins. These isotopic signatures and C2H6/CH4 ratios have been used for source discrimination in the weekly atmospheric measurements of stable CH4 isotopes over a two-month winter period at the Lac La Biche (LLB) measurement station, located in Alberta, approximately 200 km northeast of Edmonton. The average signature of −59.5 ± 1.4‰ observed at LLB is likely associated with transport of air after passing over oil industry sources located south of the station.

Highlights•Mobile and continuous measurements of stable carbon isotopes in specific CH4 source plumes in Alberta.•CH4 isotopic signatures were accurately derived using an AirCore coupled to a CRDS instrument.•The enriched isotopic values of CH4 from the natural gas industry show thermogenic origin.•The depleted isotopic values of CH4 from the oil industry show microbial origin.•Isotopic signature information will have a profound implication on modelling activities for CH4 emission estimates in Canada.